Charged particle beam systems are widely spread in the semiconductor industry. Examples of charged particle beam devices are electron microscopes such as secondary electron microscopes (SEM), electron beam pattern generators, ion microscopes as well as ion beam pattern generators. Charged particle beams, in particular electron beams, offer superior spatial resolution compared to photon beams, due to their short wavelengths at comparable particle energy.
Charged particle beam systems are used for quality evaluations and control of semiconductor processes, e.g. for inspection of critical dimensions (CD), defect review (DR), or wafer and mask defect inspection. For these tools special low voltage electron optical columns have been developed, in particular SEM-based devices, which either deliver high resolution having electron probes with nanometer and sub-nanometer diameters for CD & DR, or generate high current density electron probes for wafer & mask inspection or hot spot inspection. Because of the high demands regarding probe size and/or probe current density the focus in the electron optics development was on the optimization of the primary electron beam (PE) optics. Efforts have been made to reduce/optimize the lens aberrations (mainly spherical and chromatic aberration) as well as electron-electron interaction. Recently also some focus was directed on the SE detection, since optimized detection will improve not only the contrast which eases image analysis but also reduces image acquisition time. The latter improves throughput which is relevant in particular in electron beam inspection (EBI) and HS applications.
In this context, separation of the PE beam and the signal electron (SE) beam, including secondary electrons and backscattered electrons, has been introduced which enables an off-axis detection. The related SE beam path may be generated by a beam separator for separating the SE beam from the PE beam. SE optics may be used to shape the SE beam for detection on a detector, e.g., a segmented detector.
Even though the SE beam is separated from the PE beam by the beam separator, the space available for detector arrangements in the charge particle beam device may be limited. For extracting more information about the semiconductor processes for quality evaluation and control of such processes, the detector arrangements become more complex and may tend to be larger, making the problem of space limitations more pronounced.
Consequently, there is a need for an improved charged particle beam device and method of operating the same.